<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <button id="btn">点我</button>
<script type="text/html">
     var num = 3;
     (function () {
         (function () {
             (function () {
                 var num = 2;
                 age.log(age);
                 (function () {
                     var age = 18;
                     console.log(num);
                 })();
             })();
         })();
     })();
</script>
<script>
    (function () {
        var btn = document.getElementById("btn");
        var btn1 = document.getElementById("btn");
        var btn2 = document.getElementById("btn");
        var btn3 = document.getElementById("btn");
        var btn4 = document.getElementById("btn");
        btn.onclick = function () {
            alert(0);
        }
    })();

    (function () {
        var d = document;
        var btn = d.getElementById("btn");
        var btn1 = d.getElementById("btn");
        var btn2 = d.getElementById("btn");
        var btn3 = d.getElementById("btn");
        var btn4 = d.getElementById("btn");
    })();

    (function (document) {
        var btn = document.getElementById("btn");
        var btn1 = document.getElementById("btn");
        var btn2 = document.getElementById("btn");
        var btn3 = document.getElementById("btn");
        var btn4 = document.getElementById("btn");
    })(document);

    /*var num = 0;
    for(var k in window){
        num++;
        document.write(k + "," + num + "<br/>")
    }*/
</script>
</body>
</html>